Las Vegas investigators have given more details about the deadliest shooting in modern US history as they described how the gunman opened fire on airport fuel tanks and on police officers arriving at the massacre.

Mandalay Bay hotel staff did not notify Las Vegas police about a shooting in a hallway until after Stephen Paddock opened fire on the crowd outside at a country music festival, a federal official said.

Investigators have met the brother of the Las Vegas gunman while friends and relatives of the 58 killed and other concert-goers returned to the scene to reclaim shoes, phones and bags left behind in the panic as they fled.

The "bump stocks" device that the Las Vegas gunman used to turn semi-automatic rifles into fully automated weapons should be "subject to additional regulations", the National Rifle Association has said.

Through tearful stories of last moments together and in heart-wrenching tributes, relatives and friends have been remembering the dozens of people killed in the shooting massacre on the Las Vegas strip.

The man who killed 59 people and injured 527 others in a mass shooting in Las Vegas was a big-spending gambler who took 23 guns into his hotel room before opening fire on crowds attending an outdoor music festival.